Excess-voltage protective device



3,064,156 EXCESS-VOLTAGE PROTECTIVE DEVICE Ralph R. Pittman, 5324 Southwood Road,

Little Rock, Ark. Filed Dec. 14, 1950, Ser. No. 75,763 Claims. (Ci. 313Z31) This invention relates generally to lightning protective devices adapted for use in connection with energized electrical circuits for the purpose of limiting the voltage rise which may be impressed on an associated conductor by lightning strokes or otherwise.

The principal object of the invention is the provision of a voltage-responsive device having an advantageously low spark-over voltage combined with a high current interrupting ability, the current interruption being assisted by quickly moving the are away from the initial sparkover path to a remote and relatively much longer path, thereby cooling the arc to facilitate its rapid extinguishment.

A more specific object is the provision of an expulsion lightning protective device embodying a filler member provided with a helical groove for receiving the arc-generated conducting gases and thus elongating the arc therealong, the filler being provided with a novel electrode arrangement for realizing a greatly reduced spark-over voltage in comparison with known types of spiral-groove constructions, while at the same time retaining the wellknown favorable arc-extinguishing characteristics of helically-grooved filler constructions.

Another object of the invention is the provision of means for shielding one of the two spaced electrodes forming the weakest and preferred spark-over gap within the device by an arrangement in which the initial arc terminating thereon is instantly driven therefrom, thereby effectively precluding the lengthening of the protective spark gap by fusing or vaporization of the electrode from the heat of the are.

With these and other objects in view which will appear from the following description, my invention resides in the novel form, combination and construction of its components, and the appended claims will define the scope of the invention.

The single FIGURE of the drawing illustrates a preferred embodiment of the invention.

The particular embodiment shown has a discharge chamber within the outer tubular insulator 30, hard fiber being one suitable construction material. The upper electrode 16, here shown as an inverted cup-shaped member, is threaded into and closes the upper end of the tubular insulator 30, and the metal upper-terminal stud 12' threadedly extends downward through the top and into the hollow of the upper electrode 16. y

In somewhat similar manner, a lower metal electrode 25 extends upwardly from the lower end of the tubular insulator 39 into and in threaded engagement therewith, and a lower terminal stud 29 extends coaxially upward in threaded engagement with the lower electrode member 25, an outwardly extending threaded portion of the stud 29 being fitted with the terminal nuts 32 and 33, for convenience in connecting a ground wire, or for use in mounting the device, if desired.

The vents 27 provide for the escape of gas which may be expanded or generated within the tubular insulator 30, and the sleeve 26 encloses a portion of the terminal stud 29 to protect it from possible damage which might attend gas discharge.

Within the tubular insulator 3! is fitted, in tight slip fit relationship, a generally cylindrical filler 19, of some insulating material such as hard fiber. The lower end of the filler 19 has fitted thereon the metal ferrule 21, the lower surface of which rests upon a matching sloped sur- 3,064,156 Patented Nov. 13, 1962 2 face formed integrally with the upper central portion of the lower electrode 25 so as to bias the filler 19 laterally against the inner wall of the tubular insulator 3tlto the left as here illustrated.

The upper end of the filler 19 is beveled to provide a matching sloped end surface in contact with the lower surface of the biasing block 18, the latter being urged downward by the compression spring 17. The filler is thus continuously urged to contact with the inner surface of the tubular insulator along a vertically and longitudinally extending line of abutment.

A narrow channel or groove 22, originating at the lower end of the filler 19 at the location designated by the numeral 23, extends helically around the filler to its upper end, the numeral 24 indicating the upper end of the groove 22. The preferred construction has a generally triangularshaped groove with an inwardly extending fiat top and an outwardly and downwardly sloping side. It is essential for best operating results that the width of the channel 22 be substantially less than the width of the land between adjacent convolutions of channel. The width of the land as here illustrated is the vertical distance between the points designated by the numerals 22 and 23.

Beginning at a point indicated by the numeral 35, which is diametrically opposed to the lower end of the groove 23, a helically formed conducting electrode 20 is embedded in the land of the filler 1?, here shown as positioned along the center-line of the land and spiraling upwardly around the tiller, terminating at the point designated by the numeral 34. The lower end of the land electrode 20 engages the upper edge of the lower electrode 25, so that the weakest electrical path through the device includes the gap between the lower edge of the upper electrode 16 and the upper end of the land electrode 20 at the point 34.

A housing 31, of porcelain or similar material, is provided to house the elements of the dicharge chamber, being supported at its lower end by the outwardly extending flange of the lower electrode 2.5, and positioned and covered at its upper end by the metal cover 14 and fastened by the nut 13 of the stud 12, the latter extending through a centrally-positioned opening in the cover 14. Gaskets 1'5 and 28 may be provided to seal the respective ends of the housing 31.

In applying the device, the upper terminal 10 is connected to the normally energized terminal of the apparatus to be protected, the external series spark gap 11 being provided in accordance with common practice to avoid possible damage from leakage current which might otherwise pass through the device. The lower terminal 29 is usually connected to ground.

' When S0 connected, upon the occurrence of a predetermined excess voltage, such as might be caused by lightning, the gap 11 and the internal gap between the upper electrode 16 and the land electrode 20 sparks over, discharging the surge to ground. The discharge spark follows a path along the abutment line of the filler 19 and the tube- 30, the path crossing the groove 22 and the intermediate land. The heat attending the discharge expands the air in the upper end of the device, and this expanded air, along with any gaseous distillation products from the fiber members, finds the groove 22 to be the only available discharge path for pressure relief. The generated gas mixture is initially highly conducting, so that any dynamo-electric 60 cycle follow current instantly forms an are extending spirally along the groove 22 from the upper electrode 16 to the lower electrode 25, thereby instantaneously shunting the land electrode 20 entirely out of the follow-current circuit.

The land electrode 2% is thus instantly relieved of any current-carrying responsibility, and at the same time the 3 are is elongated to a path several times its original length and thereby quickly cooled to extinction.

From the above descripion, it may be seen that invention retains the excellent arc-extinguishing qualities of presently available helically'grooved-filler devices, and at the same time solves the long-standing and well-recog nized undesirable high-sparkover problem inherent in known devices. The cause of his undesirable high-sipaik= over voltage, particularly on steep voltage waves, may be quickly recognized if a device as herein described is visualized with the land electrode removed. The initial spark-over distance is then the full length of the filler, from top electrode 16 to lower electrode 25. This is the construction of presently known devices, and compares to the relatively small sparkover distance of my invention.

It will be apparent from the foregoing description that modifications and variations of the present invention are possible, and that it may be practiced otherwise than as specifically described and illustrated.

I claim as my invention:

1. An excess-voltage protective device comprising an outer tubular insulator having at least one end vented, an elongated filler member of insulating material fitted within said tubular insulator, said filler member having a groove extending helieally along the surface thereof and thereby forming a helieally extending land between adjacent convolutions of said groove, the width of said land being substantially greater than the width of said groove, spaced conducting electrodes disposed at the opposite ends of said tubular insulator, and structural means for causing spark-over to occur Within said tubular insulator, said structural means including a conducting land electrode extending into said tubular insulator and terminating in spaced relationship with one of said electrodes at a point within the helieally extending land.

2. An excess-voltage protective device comprising an outer tubular insulator having at least one end vented, an elongated filler member of insulating material fitted wihin said tubular insulator, said filler member having a groove extending helieally along the surface thereof and thereby forming a helieally extending land between adjacent convolutions of said groove, means holding said filler member in lateral abutting engagement with the inner surface of said tubular insulator to provide a longitudinally extending line of abutment therebetween, spaced conducting electrodes disposed at the opposite ends of said tubular insulator, and structural means for causing spark-over to occur within said tubular insulator and along said line of abutment, said structural means ineluding a conducting land electrode extending longitudinially into said tubular insulator and terminating in spaced relationship with one of said electrodes at a point on said line of abutment and within the helieally extending land.

3. An excess-voltage protective device comprising an outer tubular insulator having at least one end vented, an elongated filler member of insulating material fitted wihin said tubular insulator, said filler member having a groove extending helieally along the surface thereof and thereby forming a helieally extending land between adjacent convolutions of said groove, means holding said filler member in lateral abutting engagement with the inner surface of said tubular insulator and forming therebetween a line of abutment extending longitudinally across both said groove and said land, spaced conducting upper and lower electrodes disposed at the opposite ends of said tubular insulator, and structural means for causing sparkov'e'r to occur within said tubular insulator and along said line of abutment, said structural means including a conducting land electrode extending longitudinally into said tubular insulator from the lower electrode and terminating in spaced relationship with the upper electrode at a point on said line of abutment and within the helieally extending land,- the gap between said last-named electrodes extending along a portion of said line of abutment crossed by both said groove and said land.

4. An excess-voltage protective device comprising an outer tubular insulator having at least one end vented, a generally cylindrical filler member of insulating material fitted within said tubular insulator, said filler member having a groove extending helieally along the surface thereof and thereby forming a helieally extending land between adjacent convolutions of said groove, means holding said filler member in lateral abutting engagement with the inner surface of said tubular insulator along a longitudinally extending line of abutment, spaced upper and lower conducting electrodes disposed at the opposite ends of said tubular insulator, and structural means for causing sparkover to occur within said tubular insulator and along said line of abutment, said structural means including a conducting electrode extending helieally along the surface of said land into said tubular insulator from the lower electrode and terminating in spaced relationship with the upper electrode at a point on said line of abutment.

5. An excess-voltage protective device comprising an outer tubular insulator having at least one end vented, a generally cylindrical filler member of insulating material fitted within said tubular insulator, said filler member having a groove extending helieally along the surface thereof and thereby forming a helieally extending land between adjacent convolutions of said groove, the width of said land being substantially greater than the width of said groove, means holding said filler member in lateral abutting engagement with the inner surface of said tubular insulator along a line of abutment extending longitudinally across said land, spaced upper and lower conducting electrodes disposed at the opposite ends of said tubular insulator, and structural means for causing spark-over to occur within said tubular insulator along said line of abutment and across said land, said structural means including a conducting electrode extending longitudinally along the spiral center-line of said land into said tubular insulator from the lower electrode and terminating in spaced relationship with the upper electrode at a point on said line of abutment.

References Cited in the file of this patent UNITED STATES PATENTS 

